Emissions of hydrocarbons and other products of incomplete combustion have become a serious problem in connection with air pollution. This problem has been the subject of extensive research and has led to many proposals for emissions control systems for use in conjunction with Internal Combustion Engines.
Problems associated with emissions control are present in all internal combustion engines, but are especially troublesome in older engines which may be less efficient than newer engines. Of course one remedy for this problem would be to simply replace the emissions control system in all older internal combustion engines, especially those in vehicles. However, this remedy may prove to be too costly to be worthwhile.
As air pollution becomes ever more important, the standards for emissions of all vehicles, especially automobiles, are made increasingly strict. Some older vehicles may not be able to meet the stricter standards, and even some new cars may have an emissions control system that is prohibitively expensive in order to meet the strict emissions control standards of many states.
While there have been many proposals for the primary emissions control system, itself, there is still a need for a cost-effective means for either improving the efficiency of the overall emissions removal or for maintaining satisfactory emissions control even if the primary emissions control system should suffer a degradation in performance or for improving the overall efficiency of the emissions control of the vehicle in order to meet standards that have been made stricter after the vehicle was originally sold. At the present time, newer, and stricter, emissions control standards are often written to exclude older vehicles. Such exclusion can vitiate the advantages gained by such stricter standards.